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BIL 250 Notes Chapters 4-5

by: Jessica Vitale

BIL 250 Notes Chapters 4-5 BIL 250

Marketplace > University of Miami > Biology > BIL 250 > BIL 250 Notes Chapters 4 5
Jessica Vitale

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These notes include information that will be on the next exam. They incorporate concepts from the video lecture, learning catalytics, and in class lectures. I will post chapters 6-7 later this we...
Dr. Wang
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This 5 page Bundle was uploaded by Jessica Vitale on Sunday September 18, 2016. The Bundle belongs to BIL 250 at University of Miami taught by Dr. Wang in Spring2015. Since its upload, it has received 27 views. For similar materials see Genetics in Biology at University of Miami.


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Date Created: 09/18/16
Chapter 4: Extensions of Mendelian Genetics Alleles and Phenotypes Wild-type – most often observed; used as a standard against less popular occurrence at a particular locus; not always dominant Mutant – less common, usually contains modified genetic information; altered gene product Loss-of-function mutation – loss of function of producing an enzyme; - Null allele leads to complete loss of function Gain-of-function mutations – increase quantity of gene product; most often result in dominant alleles Neutral mutations – result could not be detected; no change to phenotype to evolutionary fitness Incomplete dominance and codominance: the heterozygote is distinguishable Incomplete dominance: - Quantitative - Heterozygote is a mix of two alleles (intermediate phenotype) - Neither allele is dominant or recessive to the other - A cross between the heterozygotes always produces a 1:2:1 ratio o Genotypic & phenotypic ratios are the same - Ex: color dilution gene in horses - Tay-Sachs disease: fatal lipid-storage disorder, neonates die during their first 1-3 years of life o Heterozygotes are phenotypically normal but have only 50% of the enzyme activity (hexosaminidase A) found in normal individuals Codominance: - Heterozygote exhibits the phenotype of both homozygotes - Two dominant alleles expressed at the same time - Ex: human M-N blood group system - A cross between the heterozygotes always produces a 1:2:1 ratio - In a one gene/ three allele system, six different phenotypes are possible Multiple alleles: when 3 or more alleles of the same gene are present in a population - Multiple alleles can be studied only in populations - ABO blood groups Mutation of H allele  Bombay - Woman was genetically type O but functioning as type B Epistasis: gene interaction where expression of one gene can impact the function of a different gene - modified ratio of 9:3:3:1 o 9:3:4 o 12:3:1 o 9:7 o 9:6:1 o 15:1 Haplosufficiency: the dominant allele makes enough protein to offset that of the bad allele - haplo = single - Huntington disease = haplo-insufficient mutation All Normal – parents will pass down dominant allele - Each parent has the healthy phenotype for the disease they don’t have  they produce the enzyme when they have the dominant trait (Parent with PKU genotype= aaBB; Parent with AKU genotype= AAbb) - Cross the parents and all F1 will be heterozygous so they will have a dominant allele that produces the enzyme making them all normal and without the diseases. - ^example of epistasis X-linked Traits - Apparent phenotypic differences between males and females in F1 & F2 o Male phenotype depends on the X chromosome received from their mothers o If the female is heterozygous, about ½ of the male progeny will have the trait Sex Linkage – a trait controlled by a gene located on either sex chromosome - X-linked dominant o Male progeny are unaffected if only father has the trait o All female progeny would have the trait if either mother or father is affected - X- linked recessive o Ex: red-green color blindness - Y-linked - Sex-limited inheritance o The genotype may exhibit one phenotype in males and a different in females or vice versa - Sex-influenced inheritance o The expression of genes is dependent on the hormones of the individual o The heterozygous genotype exhibits different phenotypes in different sexes; example: baldness Penetrance: frequency with which individuals of a given genotype manifest some degree of a specific mutant phenotype Expressivity: range of expression of the mutant genotype Recessive lethal allele: homozygous recessive individual will not survive Dominant lethal allele: the presence of just one copy of the allele results in the death of the individual; ex: Huntington disease Epigenesis: each step of development increases the complexity of the organism or feature of interest and is under the control and influence of many genes - Example: formation of the inner ear in mammals o Mutations  hereditary deafness o Mutant phenotype = heterogeneous trait Pleiotropy: the expression of a single gene has multiple phenotypic effects - Example: Marfan syndrome Chapter 5: Gene Mapping in Eukaryotes  Position of genes plays a role in its functioning  Greater the distance of genes on a chromosome, the higher the frequency of crossing over between them  Exchanges also occur between sister chromatids but it will not create new recombinant gametes  Independent assortment occurs with gene pairs on non-homologous chromosomes  Cis configuration (coupling): alleles on the same linkage group o No exchange occurs o Complete linkage  no recombinant chromosomes  Two genes on a single pair of homologs o Exchange occurs between 2 nonsister chromatids  50% gametes are new, recombinant, different from the parent  Frequency depends on the distance between loci  Closer genes, lower frequency of recombinant chromatids  Trans or repulsion configuration  Three-point mapping method: double crossing over  Positive interference- eukaryotes  Negative interference – prokaryotes  Recombinant frequency: 1% = 1 map unit o Observed #/ Total o The map distance between any two genes is the sum of the percentages of all detectable recombination events between them  Interference o 1 – (observed frequency of double crossover / expected frequency of double crossover o Interference effects are more likely when crossovers are confined to a small region.  To construct a mapping cross of linked genes, it is important that the genotypes of all of the gametes produced by the heterozygote can be deduced by examining the phenotypes of the progeny,  The cross must be constructed so that the genotypes of all gametes can be accurately determined by observing the phenotypes of the resulting offspring  A sufficient number of offspring must be produced in the mapping experiment to recover a representative sample of all crossover classes  Frac NCO refers to the fraction of gametes that have not undergone crossing over and thus their genotypes reflect those of the parental gametes.  One parent has to be homozygous recessive and one parent has to be heterozygous to determine mapping Genes linked on the same chromosome segregate together - complete linkage: produces only parental or noncrossover gametes Mendel didn’t find linkage because some genes were linked but they were too far apart for crossing over to be distinguished from independent assortment Triple crossing over in a four point map can be predicted to be less frequent than noncrossover, sco, and dco. Genes on opposite ends of chromosomes  independent assortment  1:1:1:1 Interference: when one recombination event on a chromosome inhibits other closely linked recombination events If you have genes (A, B, & C) linked on the same chromosome you can determine gene order by looking for DCO phenotypes involving the wild type and mutant alleles of genes A, B, and C, - Determine phenotypes and proportions of progeny


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